package 二叉树;

import java.util.ArrayList;
import java.util.List;

/**
 * 590. N-ary Tree Postorder Traversal
 * https://leetcode.com/problems/n-ary-tree-postorder-traversal/
 *
 * Given an n-ary tree, return the postorder traversal(后续遍历) of its nodes' values.
 *
 * Nary-Tree input serialization is represented in their level order traversal,
 * each group of children is separated by the null value (See examples).
 *
 *
 * Follow up:
 * Recursive solution is trivial, could you do it iteratively?
 *
 * Example 1:
 *
 *           1
 *         / | \
 *        3  2  4
 *       / \
 *      5   6
 *
 * Input: root = [1,null,3,2,4,null,5,6]
 * Output: [5,6,3,2,4,1]
 *
 *  Example 2:
 *              1
 *        /  /  |   \
 *       2  3   4    5
 *         / \  |   / \
 *        6  7  8  9  10
 *           |  |  |
 *           11 12 13
 *           |
 *           14
 *
 * Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
 * Output: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]
 *
 *
 * Constraints:
 *
 * The height of the n-ary tree is less than or equal to 1000
 * The total number of nodes is between [0, 10^4]
 */
public class E_590_N叉树的后序遍历 {

    public List<Integer> postorder(Node root) {
        List<Integer> output = new ArrayList<>();
        postorderTraversal(root, output);
        return output;
    }

    public void postorderTraversal(Node root, List<Integer> list) {
        if (root == null) return;
        for (Node node: root.children) {
            postorderTraversal(node, list);
        }
        list.add(root.val);
    }

}
